crystal structure of the third signal-recognition particle GTPase FlhF reveals a homodimer with bound GTP

Flagella are well characterized as the organelles of locomotion and allow bacteria to react to environmental changes. The assembly of flagella is a multistep process and relies on a complex type III export machinery located in the cytoplasmic membrane. The FlhF protein is essential for the placement...

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Published in:	Proceedings of the National Academy of Sciences - PNAS Vol. 104; no. 34; pp. 13621 - 13625
Main Authors:	Bange, Gert, Petzold, Georg, Wild, Klemens, Parlitz, Richard O, Sinning, Irmgard
Format:	Journal Article
Language:	English
Published:	United States National Academy of Sciences 21-08-2007 National Acad Sciences
Subjects:	Active sites Amino Acid Motifs Arginine - genetics Arginine - metabolism Bacillus subtilis Bacillus subtilis - enzymology Bacillus subtilis - genetics Bacteria Bacterial Proteins - chemistry Bacterial Proteins - genetics Bacterial Proteins - metabolism Bacteriology Binding Sites Biochemistry Biological Sciences Catalysis Cell membranes Crystal structure Crystallography, X-Ray Dimerization Dimers Flagella Guanosine Triphosphate - chemistry Guanosine Triphosphate - metabolism Hydrolysis Models, Molecular Monomeric GTP-Binding Proteins - chemistry Monomeric GTP-Binding Proteins - genetics Monomeric GTP-Binding Proteins - metabolism Monomers Nucleotides Protein Structure, Quaternary Protein Structure, Tertiary Proteins Ribosomes Sequence Alignment Structural Homology, Protein
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Summary:	Flagella are well characterized as the organelles of locomotion and allow bacteria to react to environmental changes. The assembly of flagella is a multistep process and relies on a complex type III export machinery located in the cytoplasmic membrane. The FlhF protein is essential for the placement and assembly of polar flagella and has been classified as a signal-recognition particle (SRP)-type GTPase. SRP GTPases appeared early in evolution and form a unique subfamily within the guanine nucleotide binding proteins with only three members: the signal sequence-binding protein SRP54, the SRP receptor FtsY, and FlhF. We report the crystal structures of FlhF from Bacillus subtilis in complex with GTP and GMPPNP. FlhF shares SRP GTPase-specific features such as the presence of an N-terminal α-helical domain and the I-box insertion. It forms a symmetric homodimer sequestering a composite active site that contains two head-to-tail arranged nucleotides similar to the heterodimeric SRP-targeting complex. However, significant differences to the GTPases of SRP and the SRP receptor include the formation of a stable homodimer with GTP as well as severe modifications and even the absence of motifs involved in regulation of the other two SRP GTPases. Our results provide insights into SRP GTPases and their roles in two fundamentally different protein-targeting routes that both rely on efficient protein delivery to a secretion channel.
Bibliography:	ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23 Edited by Jennifer A. Doudna, University of California, Berkeley, CA, and approved July 9, 2007 Author contributions: I.S. designed research; G.B., G.P., and R.O.P. performed research; G.B., K.W., and I.S. analyzed data; and G.B. and I.S. wrote the paper.
ISSN:	0027-8424 1091-6490
DOI:	10.1073/pnas.0702570104